Drawing-table



April 1963 A. CHAUVELOT 3,087,276

' DRAWING-TABLE Filed June 28, 1961 I ALBERT CHAUVELQT INVENTOR BY AGENT United States Patent 3,087,276 DRAWING-TABLE Albert Chauvelot, 27 Rue Ren Hamon, Villejuif, Seine, France Filed June 28, 1961, Ser. No. 120,364 Claims priority, application France July 12, 1960 3 Claims. (Cl. 45-131) The invention relates to a new drawing-table and, in particular, means for balancing the board in any position.

Balancing difficulties are well known, and there have so far only been limitedly successful solutions to this problem.

Most drawing-tables are balanced by a counter-weight, the use of which involves considerable bulk in order to provide clearance for it. It must also be noted that the cost price of the unit is usually high because of the price of the considerable load required.

It has been proposed heretofore to replace the counterweight by .a spring whereof one end is fixed to a lower cross-member of the framework of the table, and the other to an extension of the supporting arm of the board, in the immediate vicinity of the horizontal rocker-axis pin.

The chief fault of this system is that operation i hard and often laborious.

The invention relates to an improvement which avoids the aforementioned disadvantages, and enables a drawingtable of very limited bulk to be embodied.

The drawing-table, according to the invention, comprises a support frame, a horizontal rocker-axis pin forming a fixed fulcrum thereon, two par-allelogrammatic linkages articulated by apices to the pin, and a board fixed to one of the sides of the parallelograms. The sides of the parallelograms, which are articulated to the rockeraxis pin, are respectively provided with independent variable-profile cams, to which are fixed cables secured elsewhere to springs linked to the frame.

Since each parallelogram has two sides articulated to the said axis, there are therefore altogether four cams having similar functions in pairs, two of the said cams imparting balance to the table in height, while the other two impart balance to the table in inclination, at any height.

It is nevertheless clear that there might be cams on only one of the parallelograms, with balance in height and in inclination being provided by two cams only.

The above and other objects, features and advantages of the present invention will become more readily apparent from the following description and the accompanying drawing in which- FIGURE 1 is a diagrammatic view of a table according to the invention, illustrating the board and one of the two parallelogrammatic linkages; and

FIGURE 2 illustrates the cams on a larger scale.

As may be seen in these figures, this table essentially comprises a board T, a frame F, shown to have a lower cross-member S, a horizontal rocker-axis pin A and two deformable parallelograms linking the board T to the pin A. Each parallelogram comprises a side GB and another side PB, which are independently articulated to the pin A. Another side B links the end of PB to the board T. The board T is articulated to the ends of GB and B.

A cam C1 is fixed to the side GB and a cam C2 is fixed to the arm PB; the cables F1 and F2 respectively bear against these peripherally grooved independent cam-s, one end of each cable being fixed to the corresponding cam, while the other end is fixed to a spring R1 or R2. These springs are fixed elsewhere to the cross-member S.

As may be seen in FIGURE 2, the said cams C1 and C2 have a profile, which may be defined as below, at least as regards their general aspect.

3,087,276 Patented Apr. 30, 1963 If the distance A01 (or A02) is given a value of l, the distance AMI (or AM2) will be greater than AOl (or A02), while the distance AMI (or AM2) will be much less than the distance A01 (or A02).

To sum up, the profile passes through a point (M1 01' M2) of maximum distance from the centre of rotation A for a mean position of height and inclination.

It will be noted that this construction. causes a variation in the point at whch the cables F1 and F2 come to bear against the cams, altering the length of the effective lever arms relative to the points of contact. In this way, the action of the spring R1 always counterbalances the vertical force applied to the board (balance in height) and the spring R2 counterbalances the rearward rocking force (balance in inclination).

'I he profile of these cams may be obtained mathematically starting from the following two increasing functions: the sinusoidal function of the loads, the linear function of the resistance of the spring.

According to the invention, these functions are matched by varying the radii normal to the tangent of the corresponding cable.

What I claim is:

1. In a drawing table, in combination, a support, an arm articulated to said support at a fixed fulcrum for rotation about a substantially horizontal axis, :a drawing board articulated to said arm for rotation therewith about said axis, a sector fixed to said arm and formed with an arcuate surface having successive portions progressively spaced from said axis, a flexible member secured to said sector and engageable with said successive portions of said surface, and spring means connected to said support and bearing upon said flexible member for applying to said arm a variable moment about said axis opposite to the moment about said axis of the load of said board applied to said arm, thereby balancing the said board.

2. The combination according to claim 1 wherein said arm constitutes part of a parallelogrammatic linkage pivotally mounting said board on said support, said linkage including a further arm fulcrumed for rotation about said axis, a link member pivoted to said further arm and articulated to said board at a location spaced from its articulation to the first-mentioned arm, said arms and said link member lying in a substantially vertical plane, a second sector fixed to said further arm and formed with an arcuate surface having successive portions progressively spaced from said axis, a second flexible member secured to said second sector and engageable with the successive portions of its surface, and second spring means connected to said support and bearing upon said second flexible member for applying to said further arm avariable moment about said axis opposite to the moment about said axis of the load of said board applied to said further arm.

3. The combination according to claim 2 wherein said arcuate surface of each of said cams has an intermediate portion of maximum distance from said axis flanked by a portion of progressively increasing distance from said axis and a portion of progressively decreasing distance from said axis.

References Cited in the file of this patent UNITED STATES PATENTS 2,988,843 Knudsen June 20, 1961 FOREIGN PATENTS 6,396 Netherlands Jan. 16, 1922 843,383 Great Britain Aug. 4, 1960 

1. IN A DRAWING TABLE, IN COMBINATION, A SUPPORT, AN ARM ARTICULATED TO SAID SUPPORT AT A FIXED FULCRUM FOR ROTATION ABOUT A SUBSTANTIALLY HORIZONTAL AXIS, A DRAWING BOARD ARTICULATED TO SAID ARM FOR ROTATION THEREWITH ABOUT SAID AXIS, A SECTOR FIXED TO SAID ARM AND FORMED WITH AN ARCUATE SURFACE HAVING SUCCESSIVE PORTIONS PROGRESSIVELY SPACED FROM SAID AXIS, A FLEXIBLE MEMBER SECURED TO SAID SECTOR AND ENGAGEABLE WITH SAID SUCCESSIVE PORTIONS OF SAID SURFACE, AND SPRING MEANS CONNECTED TO SAID SUPPORT AND 